1. Field of the Invention
The present invention relates to a cylinder apparatus adapted to move a piston by a fluid pressure, and more specifically to an apparatus of the type having one end side of the piston communicated with an outside through a breathing passage.
2. Description of Prior Art
Generally, a cylinder apparatus has a piston inserted into a cylinder bore of a housing, a first chamber defined on one end side of the piston communicated with an outside of the housing through a breathing passage, and a second chamber defined on the other end side of the piston, which a pressurized fluid is supplied to and discharged from.
When the pressurized fluid is supplied to the second chamber, since the piston contracts the first chamber to increase an inside pressure of the first chamber, an air within the first chamber is flowed to an outside of the housing through the breathing passage. To the contrary, when the pressurized fluid is discharged from the second chamber, since the piston expands the first chamber by an urging force of a spring, the inside pressure of the first chamber lowers below an atmospheric pressure so that the atmosphere outside the housing flows into the first chamber through the breathing passage.
Conventionally, a filter made of wire-netting or a filter made from sintered metal is mounted to a midway portion of the breathing passage. Thereby, when the atmosphere outside the housing passes through the breathing passage, dusts within the atmosphere and foreign materials such as chips are caught by the filter so that those foreign materials can be hindered from entering the housing.
By the way, though the filter can catch solid foreign materials such as the dusts and the chips, it can't catch a liquid and a gas. Therefore, when the cylinder apparatus is used in the atmosphere charged with a corrosive liquid and/or gas, the following problems are caused.
For example, when the cylinder apparatus is used as a work clamping means of a numerically controlled lathe which uses water-miscible cutting oil, a large amount of water-miscible cutting oil is scattered around the cylinder apparatus and a large amount of misty water droplets are contained also in the atmosphere.
When the atmosphere outside the housing flows into the housing through the breathing passage, the water-miscible cutting oil and the misty water droplets easily pass through the filter and enter the housing. Since the entered water-miscible cutting oil and water droplets deteriorate and change in quality within the housing to corrode a slide surface of the cylinder bore and a slide surface of the piston, the piston becomes unable to slide smoothly. As a result, the cylinder apparatus becomes unable to be used in a short period of time.